[PATCH net] net: airoha: Fix possible TX queue stall in airoha_qdma_tx_napi_poll()

[Lorenzo Bianconi]

Since multiple net_device TX queues can share the same hw QDMA TX queue,
there is no guarantee we have inflight packets queued in hw belonging to a
net_device TX queue stopped in the xmit path because hw QDMA TX queue
can be full. In this corner case the net_device TX queue will never be
re-activated. In order to avoid any potential net_device TX queue stall,
we need to wake all the net_device TX queues feeding the same hw QDMA TX
queue in airoha_qdma_tx_napi_poll routine.

Fixes: 23020f0493270 ("net: airoha: Introduce ethernet support for EN7581 SoC")
Signed-off-by: Lorenzo Bianconi <lorenzo at kernel.org>
---
 drivers/net/ethernet/airoha/airoha_eth.c | 30 ++++++++++++++++++++++++++----
 1 file changed, 26 insertions(+), 4 deletions(-)

diff --git a/drivers/net/ethernet/airoha/airoha_eth.c b/drivers/net/ethernet/airoha/airoha_eth.c
index 9e995094c32a..e7610f36b8e4 100644
--- a/drivers/net/ethernet/airoha/airoha_eth.c
+++ b/drivers/net/ethernet/airoha/airoha_eth.c
@@ -855,6 +855,19 @@ static int airoha_qdma_init_rx(struct airoha_qdma *qdma)
 	return 0;
 }
 
+static void airoha_qdma_wake_tx_queues(struct airoha_qdma *qdma)
+{
+	struct airoha_eth *eth = qdma->eth;
+	int i;
+
+	for (i = 0; i < ARRAY_SIZE(eth->ports); i++) {
+		struct airoha_gdm_port *port = eth->ports[i];
+
+		if (port && port->qdma == qdma)
+			netif_tx_wake_all_queues(port->dev);
+	}
+}
+
 static int airoha_qdma_tx_napi_poll(struct napi_struct *napi, int budget)
 {
 	struct airoha_tx_irq_queue *irq_q;
@@ -931,12 +944,21 @@ static int airoha_qdma_tx_napi_poll(struct napi_struct *napi, int budget)
 
 			txq = netdev_get_tx_queue(skb->dev, queue);
 			netdev_tx_completed_queue(txq, 1, skb->len);
-			if (netif_tx_queue_stopped(txq) &&
-			    q->ndesc - q->queued >= q->free_thr)
-				netif_tx_wake_queue(txq);
-
 			dev_kfree_skb_any(skb);
 		}
+
+		if (q->ndesc - q->queued == q->free_thr) {
+			/* Since multiple net_device TX queues can share the
+			 * same hw QDMA TX queue, there is no guarantee we have
+			 * inflight packets queued in hw belonging to a
+			 * net_device TX queue stopped in the xmit path.
+			 * In order to avoid any potential net_device TX queue
+			 * stall, we need to wake all the net_device TX queues
+			 * feeding the same hw QDMA TX queue.
+			 */
+			airoha_qdma_wake_tx_queues(qdma);
+		}
+
 unlock:
 		spin_unlock_bh(&q->lock);
 	}

---
base-commit: 2dddb34dd0d07b01fa770eca89480a4da4f13153
change-id: 20260407-airoha-txq-potential-stall-ad52c53094e8

Best regards,
-- 
Lorenzo Bianconi <lorenzo at kernel.org>